The invention concerns a valve train of an internal combustion engine, said valve train comprising an elongate anti-rotation bridge comprising receptions spaced behind one another for receiving valve tappets configured as roller tappets, one of which tappets is arranged in each reception and is directed with a tappet roller toward a cam of a camshaft to extend at a right angle to a longitudinal axis of the camshaft while being slidably retained in the reception, said tappet being secured against rotation through anti-rotation surfaces which are configured on an outer peripheral surface of the tappet and bear against corresponding inner surfaces of the bridge within the reception.
It is known in internal combustion engines to secure a roller tappet against rotation by a plastic bridge in which the tappet is retained through surface guidance. The outer peripheral surface of the circular cylindrical tappet is configured with at least one flat surface portion that cooperates with a corresponding flat surface portion of a reception in the anti-rotation bridge. This bridge can be a plastic component. To simplify transportation and assembly of the components of the valve train, the tappets are pre-assembled on the anti-rotation bridge through a press fit at the surfaces that contact one another. However, the clamping of the tappets in the bridge that is required for mounting may also continue to exist later during engine operation so that the compensating function of a standard tappet and the switch-off movement of a switchable tappet may be impaired.
An anti-rotation bridge in which the clamping of the tappets required for mounting remains active even in subsequent engine operation when only the anti-rotation function is called for, is shown in the document U.S. Pat. No. 5,088,455 A.
In the document DE 197 12 610 A1, that shows an anti-rotation bridge of the pre-cited type for an internal combustion engine, it is explained that internal combustion engines generally comprise roller valve tappets that engage cam lobes of a camshaft. Since it is not desirable that the tappets rotate about their longitudinal axes because the rollers of the tappets must remain in the same plane as the cam lobes, the tappets are appropriately oriented in the cylinder block of the internal combustion engine with the help of suitable retaining devices, and their rotation is prevented. One example of such a retaining device is an anti-rotation bridge in whose receptions the tappets bear with their flat surface portions against corresponding flat portions of the bridge.
It is an object of the invention to create a valve train comprising an anti-rotation bridge and roller tappets adapted to be mounted therein that operates in a defined and reliable manner.
This and other objects and advantages of the invention will become more obvious from the following detailed description.
According to a first proposition, the invention achieves the above objects by the fact that the roller tappet comprises on its outer peripheral surface, raised tappet contours that engage into retention grooves of the bridge within the reception.
According to a second proposition, the invention achieves the above objects by the fact that a projecting solid bead is configured in each reception of the bridge and engages a tappet groove configured on the roller tappet.
In this way, when the bridge has been fixed in the engine block, the tappets can be pressed out of their assembly and retention position against the camshaft by installing the associated tappet push rods. The anti-rotation surfaces that are then still effective can be disposed without a pressing force or with only a small pressing force so that the compensating function and the switch-off function of the tappet are not impaired.
Examples of embodiment of the invention are illustrated in the appended drawings and will be described more closely in the following.